This invention relates to a process for separating a C.sub.2+ hydrocarbon fraction from compressed natural gas by rectification, the required temperature and pressure conditions thereof being obtained by heat exchange and engine expansion and where the rectification column is fed by condensate fractions of the natural gas.
A process of this type is described in U.S. Pat. No. 3,292,380, wherein the natural gas first is cooled by heat exchange, resulting in partial condensation. The resultant liquid phase is, after pressure reduction, in part fed to the rectifying column, and the resultant gas phase is engine expanded to the pressure of the rectification column. This process, however, is disadvantageous insofar as natural gas containing carbon dioxide requires a special preliminary process step for the removal of CO.sub.2. Otherwise, there would be the danger of solids precipitation and even clogging of the facility if operated at low temperatures. As regards the precipitation of solids, those parts of the facility especially jeopardized are those encountering the lowest temperatures or where the carbon dioxide is concentrated. In this known process, a particularly hazardous location is at the head of the rectification column, because the carbon dioxide concentration in the reflux liquid to the column as a rule will be higher than in the liquid at the turbine discharge.